On the Evolution and Observational Signatures of Cosmic Ray Electrons in Magnetohydrodynamical Simulations

Cosmic ray (CR) electrons are ubiquitous in the universe and reveal key insights into the non-thermal physics. Their synchrotron radiation, bremsstrahlung, and inverse Compton emission shed light on the interstellar medium, on galaxies and galactic outflows, on galaxy clusters, and on active galactic nuclei. Models of these emission processes can be tested against observations with magnetohydrodynamical (MHD) simulations. While dynamically important CR protons are often included in MHD simulations, CR electrons are rarely treated because their treatment requires a detailed numerical modeling of their spectra due to complex hysteresis effects. Within the scope of this work, I have developed the efficient post-processing code CREST that evolves spatially and temporally resolved CR electron spectra. This code allows a comparison of CR electron emission signatures to observations by means of multi-frequency spectra and morphology. Further, CREST enables to validate models of CR electron acceleration and to explore whether observations can be explained by leptonic or hadronic interactions. Hence, this work opens up a new capability for MHD simulations of dynamical systems that can be compared to radio, X-ray, and γ-ray observations. I apply CREST to three-dimensional MHD simulations of the supernova remnant of SN 1006. These show that a mixed leptonic-hadronic model explains best the observed γ-ray emission and that CR electrons, similar to CR protons, are preferentially accelerated in environments where the shock direction is quasi-parallel to the upstream magnetic field. In addition, the simulations show that a magnetic field amplification by a volume-filling turbulent dynamo is required and that the Bell amplification needs to be spatially confined to the shock. Both findings are necessary in order to match simultaneously radio, X-ray, and γ-ray observations

Paleocene Deposition of the Hoback Formation on the La Barge Platform of the Green River Basin�

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Ice dynamics and glacial history from remote sensing of the Seno Skyring-Seno Otway-Strait of Magellan region, southernmost Patagonia

The glacial geomorphology of southernmost Patagonia records the advance and retreat of the Patagonian ice sheet over a number of glacial cycles. The well-preserved landform assemblages and sediments that have been left behind comprise one of the longest and most complete records of Quaternary glaciations in the world. Despite this, little is known about the pre-Last Glacial Maximum (LGM) ice sheet dynamics in a number of areas, particularly around the Strait of Magellan. This study has mapped in detail the glacial geomorphology of the Seno Skyring-Seno Otway-Strait of Magellan region from a combination of Landsat and ASTER satellite imagery and oblique and aerial photographs for the purposes of reconstructing the ice sheet dynamics. A wide variety of glacial landforms have been mapped, including glacial lineations, moraine ridges, meltwater channels, outwash plains and palaeo-shorelines. The most distinct features within the study area are highly elongate streamlined glacial lineations on the western side of the Strait of Magellan. A landsystems approach has been employed in order to decipher this group of lineations and three potentially plausible landsystems are evaluated: a palaeo-ice stream, a surging glacier, and an ice-marginal terrestrial landsystem. Based on the characteristic shape, dimensions and abrupt lateral margin of the flow-set, the lateral variation in lineation length and elongation ratios, and the presence of a potentially-deformable bed, these lineations are interpreted as being diagnostic of a terrestrial palaeo-ice stream. It is suggested that the initiation of ice streaming was caused by calving into one of two ice-dammed proglacial lakes. The lakes were located within the former Seno Skyring and Seno Otway ice lobes, which are well-defined by arcuate sequences of moraine ridges. The westernmost of the lakes, proglacial Lake Skyring, is delimited by a series of palaeo-shorelines surrounding the present-day lake Laguna Blanca. The size and orientation of meltwater channels and an outwash plain suggests that proglacial Lake Skyring drained eastwards towards the Strait of Magellan in an abrupt event. The ice sheet has been reconstructed at 10 time-steps, documenting stages of both advance and retreat. An attempt has been made to place this reconstruction within the framework of the wider glacial chronology of the region. From this, it is suggested that ice stream activity contributed to the rapid deglaciation of this sector of the ice sheet during the penultimate glaciation. Future work should focus on applying fieldwork to help validate the interpretations of this study. This should include dating of the landforms and sediments that have been mapped in order to improve the pre-LGM glacial chronology of this region, which is currently poorly-constrained

Solubility studies of ultra pure transition elements in ultra pure alkali metals

Solubility of pure iron, molybdenum, niobium, and tantalum in liquid potassiu

The nature and timing of Late Quaternary glaciation in southernmost South America

The timing and extent of former ice sheet fluctuations can demonstrate leads and lags during periods of climatic change and the forcing factors responsible, but this requires robust glacial chronologies. Patagonia, in southern South America, offers a well preserved record of glacial geomorphology over a large latitudinal range that is affected by key climatic systems in the Southern Hemisphere, but establishing the timing of ice advances has proven problematic. This thesis targets five southernmost ice lobes that extended from the former Patagonian Ice Sheet during the Quaternary; from north to south: the Río Gallegos, Skyring, Otway, Magellan and Bahía Inútil – San Sebastián (BI-SSb) ice lobes. The region is chosen because there is ambiguity over the age of glacial limits, which have been hypothesised to relate to different glacial cycles over hundreds of thousands of years but yield cosmogenic nuclide exposure data dominantly < 50 ka. This contradiction is the focus of the thesis: was the sequence of glacial limits deposited over multiple glacial cycles, or during the last glacial cycle? A new geomorphological map is used to reconstruct glacial limits and to help target new dating. Cosmogenic nuclide depth-profiles through glacial outwash are used to date glacial limits whilst accounting for post-depositional processes. These reveal that limits of the BI-SSb lobe hypothesized to date from MIS 12 (ca. 450 ka) and 10 (ca. 350 ka) were actually deposited during the last glacial cycle, with the best-dated profile giving an MIS 3 age of ca. 30 ka, indicating an extensive advance prior to the global Last Glacial Maximum (gLGM). A glacial reconstruction indicates that this may not have been unique to the BI-SSb lobe, and a compilation of published dates reveals that similar advances during the last glacial cycle indicate related forcing factors operating across Patagonia and New Zealand

MAGNETOHYDRODYNAMIC SIMULATIONS OF BLACK HOLE ACCRETION

Black holes embody one of the few, simple, solutions to the Einstein field equations that describe our modern understanding of gravitation. In isolation they are small, dark, and elusive. However, when a gas cloud or star wanders too close, they light up our universe in a way no other cosmic object can. The processes of magnetohydrodynamics which describe the accretion inflow and outflows of plasma around black holes are highly coupled and nonlinear and so require numerical experiments for elucidation. These processes are at the heart of astrophysics since black holes, once they somehow reach super-massive status, influence the evolution of the largest structures in the universe. It has been my goal, with the body of work comprising this thesis, to explore the ways in which the influence of black holes on their surroundings differs from the predictions of standard accretion models. I have especially focused on how magnetization of the greater black hole environment can impact accretion systems

Numerical analysis of a fluid droplet subject to acoustic waves

Efficient and rigorous acoustic solvers that enable high frequency sweep application over a wide range of frequencies are of great interest due to their practical importance in many engineering, physical problems or life science research that involve acoustic radiation, such as engine noise analysis, acoustic simulation in micro-fluidics and the design of lab device, etc. There is room for reduction of cost on experimental systems that can be investigated and optimised through numerical modelling of physical processes on the micro-scale level. The major difficulty that arises is the inconsistency of materials, time scales and fast oscillation nature of the solution that leads to unstable results for conventional numerical methods. However, analytical solutions are infeasible for large problems with complex geometries and sophisticated boundary conditions. Hence, the vital need for efficient solvers. In this research the development of computational methods for acoustic application is presented. The proposed method is applied to the study of propagating waves in particular to simulate acoustic phenomena in micro-droplet actuated by leaky Surface Acoustic Waves on a lithium niobate (LiNbO3) substrate. Explicitly, we introduce a new computational method for the analysis of fluids subjected to high frequency mechanical forcing. Here we solve the Helmholtz equation in the frequency domain, applying higher order Lobatto hierarchical finite element approximation in H1 space, where both pressure field and geometry are independently approximated with arbitrary and heterogeneous polynomial order. Meanwhile, a time dependent acoustic solver with arbitrary input signals is also proposed and implemented. The development of extended computational methods for the solution of the Helmholtz equation with polychromatic waves is presented, where Fourier transformation is applied to switch the incident wave and solution space from the frequency domain to the temporal domain. Consequently, the implementation and convergence rate of the numerical methods are demonstrated with benchmark problems. The numerical method is an extension of the conventional higher order finite element method and as such it relies on the definition of basis functions. In this work we implement a set of basis functions using integrated Legendre polynomials (Lobatto polynomial). Two type of basis functions are presented and compared. Therefore, the significant improvements in efficiency is demonstrated using a Lobatto hierarchical basis compared with a Legendre type basis. Moreover, a novel error estimation and automatic adaptivity scheme is outlined based on an existing a priori error estimator. The accuracy and efficiency of the proposed object oriented (predefined error level) a priori error estimator is validated through numerical assessments on a three-dimensional spherical problem and compared with uniformly h and p adaptivities. The simple and generic features of the proposed scheme allow fast frequency sweeps with low computational cost for multiple frequencies acoustic application. The current finite element approach is executed in parallel with pre-partitioned domain, which guarantees the optimal computational speed with minimal computational effort for large problems. Overall, the benefits of using the proposed acoustic solver is explained in detail. Finally, we illustrate the model's performance using an example of a micro-droplet actuated by a surface acoustic wave (SAW), which has vast applications in micro-fluidics and micro-rheology at high frequency. Conclusions are drawn, and future directions are pointed out. The proposed finite element technology is implemented in the University of Glasgow in-house open-source finite element parallel computational code, MoFEM (Mesh Oriented Finite Element Method). All algorithms and examples are publicly available for download and testing